A wine is balanced when all the component parts, such as tannins, fruit, acidity and possibly sweetness, are correctly matched and in harmony, and none stands out inappropriately. It's a bit of a subjective call.
Found on http://www.encyclo.co.uk/local/20433

1) Having a pleasing amount of low frequencies compared to mid-range frequencies and high frequencies. 2) Having a pleasing mixture of the various instrument levels in an audio recording. 3) Having a fairly equal level in each of the stereo channels. 4) A method of interconnecting electronic gear using three-conductor cables.
Found on http://www.encyclo.co.uk/local/20447